[Lonnie A]

The way I do it is to export the surface to a xml file and then in GIS use the landxml tool to create a tin in GIS. Then convert that tin to a raster for use in RAS.

[Lonnie A]

If I need to get some subsurface flow accounting I’ll typically use a storage area connector with culverts for the pipes. Requires be to “burn” in the manhole into the terrain to meet the minimum cell elevation being equal to or lower than the culvert flowline. If you play with the n value and entrance/exit loss coefficients you can adjust some of the losses to match a typical storm sewer calc. Gets cumbersome though if you need to model a lot of storm sewer.

[Lonnie A]

I’m guessing you are running the full momentum equation and seeing the effect of super elevation around the curve.

[Lonnie A]

Your analysis is correct. It’ll use the cell that correspondss to the station of the gate for control. They had to pick something to pull the data from and easiest was to use the lowest cell for reporting which usually would be the one you’d want when you have a culvert.

[Lonnie A]

I believe it is just exporting using the info from the projection file. Never needed to try it and don’t know if GIS will read a Z attribute as anything but length?

[Lonnie A]

This is how I do it. I’m not a microstation person so I have others do the export for me and it works coming from ACAD the same way:
Export from microstation the TIN as a LANDXML then in GIS use the LANDXML file to import the TIN. Then under Arc Toolbox > 3D Analyst > Conversion > TIN to Raster: Give the output tin a name with a .tif extension. I keep the output type and method as default. Under sampling distance select the cellsize option and set the number to the size you want.

[Lonnie A]

In the geometry editor under “edit” select move object and select the end of your 1D reach and move that point to be within the storage area. Once you do that you should get a message asking if you want to connect the two.

[Lonnie A]

you can insert a base flow hydrograph into the 2D flow area. Use the SA/2D Area BC Lines tool. Say you want a 200cfs base flow. Draw the BC line down the channel and in the flow editor manually enter the flow to assign to the BC line. Start your run time to start how ever long before your rainfall.

[Lonnie A]

try increasing your initial conditions flow and run a warm up period. I usually set a minimum flow on my top hydrograph ~5% of my 100yr flow. Other thing to try is setting htab to start at min channel elevation and have a fairly defined HTab.

[Lonnie A]

you’ll have to probably upload some more info as not much info to go on. sounds like a stability issue. Try a shorter time step.

[Lonnie A]

Modeling bridges with large culverts is difficult in 2D. Stability is especially difficult when your culvert is very large. In one time step the culvert can carry a significant amount of volume in comparison to the cells it is attached to.

With a large culvert, or really any culvert, modeled as a internal storage area connector you want to try and have cells a large as you can at the culvert connection to improve volume balance through time steps.

You might try to adjust the entrance and exit losses but at 0.3/0.5 I think you are in the right realm. Lowest would be maybe 0.2/0.3.

With the limitation in 2D modeling for bridges right now I would try to build a 1D/2D model so you can have the bridge in 1D with connection to the 2D.

[Lonnie A]

I typically estimate the EGL slope from the terrain slope in the area where the flow is expected to be most concentrated. After your first run you can look at the WSE slope in the area to see if adjustment to you initial estimate is necessary.

[Lonnie A]

Its hard to see from the images but if the highlighted area at the bottom of the plan view is the connector you are showing then I believe you have used a storage area connector as the boundary and the “to” and “from” are to the same 2D area? If so there is no where for the flow to go but in a circle. You need to add something for the downstream area to outfall into. If tailwater is not going to impact the outfall structure you could add a simple area times depth storage area for the “to” portion of the connector to tie to. Just make the area very large and the elevation low so it doesn’t backwater the structure.

[Lonnie A]

I’ve relayed this to HEC and believe it’s been fixed in v506…when that comes out I’m not certain. Usually I just have to move one boundary end point slightly for it to recognize the proper location. This is the same fix I use often for when I get a odd non-descript fortran error of red text right at the start of a run.

[Lonnie A]

it will read directly from the terrain if modeled in 2D.

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